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A STUDY  OF  SOME  OF  THE  TOXIC  COMPOUNDS 

OF  SELENIUM 

BY 

FLORA  MARION  LOUGEE 

A.  B.  Bates  College 
1914 


THESIS 

Submitted  in  Partial  Fulfillment  of  the  Requirements  for  the 

Degree  of 

MASTER  OF  ARTS 
IN  CHEMISTRY 

IN 

THE  GRADUATE  SCHOOL 

OF  THE 

UNIVERSITY  OF  ILLINOIS 
1921 


\t£\ 

u'S'S.B 


Csi 

Ol~ 

UJ 

CO 

QC 

r*) 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


June  2, 


192L 


I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 

SUPERVISION  BY TOIL  LQUGKE  — 

ENTITLED A.  .STUDY  Off  SOME,  QJ1 THE  TCLKIC  , COMPOUNDS  Off 


BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF Master  o£-  Arts  irnCneir, jjstry 


Recommendation  concurred  in* 


Committee 


on 


Final  Examination* 


^Required  for  doctor’s  degree  but  not  for  master’s 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/studyofsomeoftoxOOIoug 


An  Acknowledgement . 

(The  experimental  work  described  in  this 
thesis  was  carried  out  under  the  direction  of 
Dr.  B.S. Hopkins,  Head  of  the  Division  of  Inor- 
ganic Chemistry,  whose  ever  ready  interest  and 
advice  were  an  unfailing  source  of  inspiration 
and  encouragement . Thanks  are  also  due  Dr.  W. 
A. Ruth,  assistant  Professor  of  Pomology,  for 
his  kindly  assistance  in  the  matter  of  field 
tests  for  the  materials  prepared. 


1 


Table  of  Contents. 

page 

I.  Introduction  . 

A.  Nature  of  Research  Problem  

1.  Object. 

2.  Origin 

3.  Limitation  of  field  of  investigation 

B.  Preparation  for  Experimental  Work  

1.  Study  of  literature  relative  to  lime-sulfur 

a.  Preparation 

b.  Chemical  composition 

c.  Properties 

d.  Uses 

II.  Description  of  Experimental  Work  

A.  Lime-Sulfur  

1.  Preparation 

2.  Analysis 

B.  Lime-Selenium  Solution  

1.  Unsuccessful  experiments,  using 

a.  Gray  selenium 

(1)  Use  of  a modified  lime-sulfur  formula 

(2)  Fusion  of  selenium  and  calcium 

b.  Red  Selenium 

(1)  Use  of  a modified  lime-sulfur  formula 

2.  Successful  experiments,  using 

a.  Gray  selenium 

(1)  Use  of  a modified  lime-sulfur  formula 

(a)  Attempts  at  analysis 

(b)  Effect  of  varying  proportions 


O)  to 


' 


(c)  Properties 


2 

pages 


(x)  Lab  tests 

( y ) Field  tests 

C.  Soda-Selenium  Solution  12 

1.  Preparation 

2.  Properties 

D.  Atomic  Selenium  13 

1.  Field  tests 

E.  Ammonium  Polyselenide  13 

1.  Preparation 

2.  Properties 

P.  Colloidal  Selenium  14 

1.  Preparation 

2.  Properties 

a.  Lab  tests 

b.  Field  tests 

III.  Conclusions  15 

A.  Significance  of  results 15 

B.  Future  possibilities  15 

1.  Modifications  of  earlier  experiments 

2.  Extension  of  previous  work 

3.  Pests  with  ammonium  polyselenide 

4.  Tests  with  carbon  diselenide 

IV.  Summary 16 


A Study  of  Some  of  the  Toxic  Compounds 
of  Selenium. 


3 


I 

Introduction. 

A.  Nature  of  Research  Problem: 

The  object  of  the  research  here  described  was  an  investigation 

of  selenium  compounds  which  gave  promise  of  exhibiting  toxic  powers, 

The  idea  for  this  problem  grew  out  of  a careful  consideration  of 

the  close  analogy  between  the  physical  and  chemical  properties  of 

selenium  and  sulfur  and  a realisation  of  the  limitations  of  the  sul- 
fur 

compounds  at  present  employed  as  insecticides  and  fungicides. 

It  is  a well-known  fact  that  selenium  and  its  compounds  are, 
in  general,  more  toxic  than  sulfur  and  its  compounds,  and  this  tox- 
icity of  selenium  has  been  the  subject  of  considerable  investiga- 
tion in  biological  and  physiological  fields;  but  no  attempts  have 
apparently  been  made  to  try  the  effect  of  substituting  selenium  for 
sulfur  in  the  insecticides  and  fungicides  now  in  use.  In  the  re- 
search here  described,  the  effect  of  such  a substitution  was  studied 
in  the  hope  that  selenium  might  prove  superior  to  sulfur  in  appli- 
cations of  this  kind. 

Since  the  properties  of  selenium  and  sulfur  are  very  closely 
allied,  as  previously  stated,  it  will  not  be  necessary  to  discuss 
the  history  of  selenium  and  its  compounds.  Y/e  will  merely  note  in 
passing  that  selenium,  like  sulfur,  occurs  in  three  allotropic 
forms:  (1)  Liquid  selenium,  of  which  there  are  three  varieties, -- 

viz.,  the  vitreous,  the  amorphous  and  colloidal  selenium;  (2)  cry- 
stalline, red  selenium;  and  (3)  crystalline,  gray  or  metallic  selen- 
ium, which  was  the  material  that  constituted  the  basis  of  the  pres- 
ent experiments. 


i 

• 

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4 


B.  Preparation  for  Experimental  Work: 

The  first  selenium  preparation  to  be  attempted  was  a lime- 
selenium  solution  corresponding  to  the  commercial  'lime-sulfur.” 

In  order  to  understand  Just  what  experimental  conditions  would 
be  most  desirable,  a study  of  the  methods  of  preparation,  the  chem- 
ical composition,  the  properties  and  uses  of  lime-sulfur  was  un- 
dertaken. 

The  formulas  for  the  preparation  of  the  lime-sulfur  sprays 
now  on  the  market  are  numerous,  the  ratio  of  lime  to  sulfur  vary- 
ing from  1:2  to  1:2.25.  There  is  a like  variation  in  the  direc- 
tions as  to  proper  methods  of  mixing,  length  of  boiling,  etc.; 
but  we  will  here  confine  our  attention  to  the  procedure  followed 
in  the  preparation  of  one  of  the  standard  commercial  lime-sulfurs. 

Water  is  added  to  fifty  pounds  of  quicklime  in  sufficient 
quantity  to  start  vigorous  action  and  before  the  heat  of  slaking 
is  dissipated,  a hundred  pounds  of  sulfur  are  stirred  in.  More 
water  is  then  added  to  make  the  volume  up  to  fifty  gallons  and  the 
mixture  is  boiled  for  about  forty-five  minutes,  the  water  lost  by 
evaporation  being  replaced  from  time  to  time  as  needed.  The  re- 
sulting solution  on  dilution  to  one  hundred  gallons,  is  ready  for 
spraying  purposes. 

Although  the  literature  on  the  general  subject  of  lime- sulfur 
is  voluminous,  the  real  chemical  investigations  have  been  few. 
Perhaps  the  men  who  have  contributed  most  to  our  meager  knowledge 
of  the  chemistry  of  lime-sulfur,  are  Avery  (Bull. 90,  Bureau  of 
Ghem. , U.S.  Dept,  of  Agr. ) ; Haywood  (Jour.  Amer.  Chem.  Soc.  27, 

244  and  Bull,  101,  Bureau  of  Ghem.,  U.S.  Dept,  of  Agr.);  Thatcher 
(Bulls.  56  and  76,  Wash.  Agr.  Exp.  Sta. ; Jour.  Amer.  Chem.  Soc. 


* 


. 





< 


5 


30,  63);  Giboney  (Cir.  no.  1.,  Virginia  State  Crop  Commission); 
Wellington  (Bull.  116,  Mass.  Agr.  Exp.  Sta. ) ; Van  Slyke  (Bull.  329, 
U.Y.Agr.  Exp.  Sta.,  Geneva);  Stewart  (Bull.  99,  Penn.  Agr.  Exp. 
Sta.);  Harris  (Tech.  Bull.  6,  Mich.  Agr.  Exp.  Sta.);  Shafer  (Tech. 
Bull,  no  11,  Mich. Agr.  Exp.  Sta.);  Thompson  and  Whittier  (Bull, 

105,  Delaware  Agr.  Exp.  Sta.);  Tartar  and  Bradley  (Jour.  Ind.  Eng. 
Chem.  2,  271);  Tartar  (Research  Bull.  no.  3,  Oregon  Agr.  Exp.  Sta.); 
Chapin  (Bull.  no.  451,  U.S.Dept.  ox  Agr.);  and  Winter  (Jour.  Ind. 
Eng.  Chem.  10,  545). 

In  the  earlier  investigations  here  referred  to,  there  is  con- 
siderable disagreement  as  to  the  exact  nature  of  the  chemical  re- 
actions involved  in  the  manufacture  of  lime-sulfur  solution;  but 
among  the  more  recent  investigators,  Tartar,  Thompson  and  Whittier, 
and  Chapin,  the  differences  of  opinion  are  few.  According  to  these 
men,  the  primary  reaction  that  occurs  when  the  ratio  of  lime  to 
sulfur  is  1:2,  is  represented  by  the  following  equation: 

3Ca( OH  )g  4 10S  - — > 2CaS4  4 CaS20^  4 SH^O. 

When  the  ratio  of  lime  and  sulfur  is  1:2.25,  the  main  reaction  is: 

3Ca( OH) g 4 IPS  * 2Ca3205  4 3HgO. 

In  most  cases  it  is  probable  that  the  lime-sulfur  solution  contains 
a mixture  of  the  tetra-  and  penta-sulfides . 

The  valuation  of  lime-sulfur  as  an  insecticide  has  been  made 
the  subject  of  an  exhaustive  investigation  by  Shafer.  (Tech.  Bull, 
no. 11,  Mich.  Agr.  Exp.  Sta.).  His  work  strongly  indicates  that 
the  insecticidal  value  of  lime-sulfur  solution  is  due  principally 
to  the  following  properties:  (l)Its  power  to  take  up  large  amounts 
of  oxygen,  thus  causing  the  insects  treated  to  suffer  from  an  in- 
sufficient supply  of  this  element. 


(2)  Its  ability  to  soften  the  newly  secreted  wax  (a  property  which 
is  probably  intimately  connected  with  the  poly sulfides  present). 

(3)  The  amount  of  free  sulfur  formed  in  its  decomposition. 

If  these  conclusions  are  correct,  the  value  of  lime-sulfur 
as  an  insecticide  is  largely  dependent  upon  the  following  reactions: 
CaSg  4 30  — > CaSsOg  4 33 

CaS4  + 30  » CaS^Qg  + 23 

CaS£0g  — > CaSOg  + S 

CaSOg  4 0 - ■ CaS04 

Besides  its  use  against  scale  insects  such  as  the  San  Jose/ 
scale,  lime-sulfur  is  now  employed  in  a wide  variety  of  ways.  It 
has  given  good  results  against  aphis,  blight,  apple  scab,  larvae 
of  fall  webworm,  caterpillars,  etc.  It  has  also  been  used  quite 
expensively  as  a sheep  and  cattle  dip. 

II. 

Description  of  Experimental  Work. 

A.  Lime -Sul fur  Solution: 

Preparation. 

In  order  to  become  acquainted  with  the  technique  that  is  re- 
quired in  the  preparation  of  insecticides  in  general,  a sample  lime- 
sulfur  solution  was  prepared  in  accordance  with  the  formula  previous- 
ly given. 

Analysis . 

The  solution  was  analysed  by  a combination  of  the  methods  em- 
ployed by  Tartar  and  Harris.  In  preparing  the  samples  for  the  ti- 
trations, lOcc  of  the  filtered  lime-sulfur  solution  was  diluted 
to  lOOcc,  and  lOcc  aliquots  used  for  the  analyses.  Each  aliquot 
v;a3  diluted  with  30cc  of  distilled  water  before  the  titrations  were 


- 


7 


made.  The  determination  of  the  "poly sulfide  sulfur"  was  made  by 
titrating  with  decinormal  HG1,  using  methyl  orange  as  indicator; 
the  "sulfide  sulfur"  was  determined  by  titrating  with  ammoniacal 
zinc  chloride,  usinp:  nickel  sulfate  as  indicator;  and  the  "total 
sulfur”  was  determined  by  oxidising  with  UagOg  and  precipitating 
and  weighing  as  barium  sulfate. 

As  the  results  of  the  foregoing  analyses  agreed  in  every  par- 
ticular with  the  composition  consigned  to  lime-sulfur  by  Tartar 
and  others,  the  chemical  reactions  previously  given,  as  the  most 
probable  primary  reactions  between  lime  and  sulfur, were  accepted 
as  correct  and  we re  made  the  basis  of  the  formula  to  be  used  in 
the  x:I*ePa'ta'ti°n  of  an  analogous  lime -selenium  solution. 

B.  Lime-Selenium  Solution: 

Unsuccessful  Experiments. 

Acting  on  the  assumption  that  lime  and  selenium  under  condi- 
tions analogous  to  those  observed  in  the  preparation  of  a lime-sul- 
fur solution,  whould  react  in  accordance  with  the  following  equa- 
tion : 

3Ca( OH ) 0 + lOSe  — * 3CaSe4  f GaSegOg  f 3HgO. 

11.35  gms.  of  quicklime,  56  gms.  of  gray  selenium  and  lllcc  of  wa- 
ter were  boiled  together  in  an  open  vessel  over  a Bunsen  flame,  for 
one  hoar  without  any  apparent  chemical  reaction.  Only  amechanical 
mixture  of  selenium  and  lime  was  left  in  the  vessel. 

In  the  next  attempt  at  preparation  of  a lime-selenium  solution, 
quicklime  (made  by  calcining  calcium  carbonate),  gray  selenium  and 
water  in  the  same  proportions  as  before  were  refluxed  over  a Bunsen 
flame  for  twelve  hours  without  any  apparent  effect. 

Gray  selenium,  and  metallic  calcium  in  the  right  proportions 


•« 


. 


\ 


8 


for  the  formation  of  calcium  pentaselenide  Ca:  5gms.  Se ) 

were  next  fused  in  a covered  crucible.  The  product  was  a hard 
st6el-gray  substance  of  metallic  luster,  suggestive  of  a calcium- 
selenium  alloy.  The  solubility  of  this  product  was  very  slight  as 
it  was  apparently  unaffected  by  long-continued  boiling  with  water. 
When  dropped  red-hot  into  cold  water,  it  assumed  the  form  of  di- 
minutive pellets  which  were  slowly  decomposed  on  long  standing  with 
water  on  a closed  flask,  as  shown  by  the  mulberry  shade  developed 
by  the  water  and  the  disagreeable  odor  resembling  that  of  CSg  which 
was  evolved  whenever  the  flask  was  uncorked. 

The  next  variation  from  the  original  procedure  consisted  in 
the  substitution  of  red  selenium  for  the  gray.  The  red  selenium 
for  this  purpose  was  prepared  by  passing  chlorine  gas  into  a water- 
suspension  of  gray  selenium;  adding  strong  HC1  to  reduce  the  selen- 
ic  acid  thus  formed  to  selenious  acid;  and  precipitating  red  selen- 
ium from  the  solution,  by  means  of  sulfur  dioxide.  The  red  selen- 
ium was  filtered,  washed  thoroughly  with  distilled  water,  and  dried 
in  a desiccator  over  sulfuric  acid.  This  red  selenium,  which  had 
become  plum-colored  after  standing  for  several  days,  was  mixed  in 
the  usual  proportions  with  water  and  lime  (prepared  by  calcining 
CaCO 3)  and  heated  on  a steam  bath  for  exactly  one  hour.  The  only 
apparent  change  was  a reversion  of  the  red  selenium  to  the  gray  va- 
riety. No  lime-selenium  solution  was  formed. 

Successful  Experiments. 

In  the  meantime,  a better  grade  of  quicklime  was  procured,  and 
one  of  the  earlier  attempts  at  preparation  of  a lime-selenium  solu- 
tion by  use  of  gray  selenium  and  the  modified  lime-sulfur  formula 
was  repeated.  One  gram  of  the  quicklime  was  fused  for  about  an  hour 


9 


with  5.65  gras,  of  gray  selenium,  the  resulting  product  finely  po  - 
d6red,  and  about  50  cc  of  boiling  water  poured  upon  it.  A deep 
wine-red  solution  was  immediately  produced,  indicating  that  the 
lime  and  sulfur  had  reacted  at  last. 

Analysis . 

Some  attempts  were  made  to  analyse  the  lime-selenium  solution 
by  the  methods  previously  used  in  the  analysis  of  lime-sulfur;  but 
the  lime-selenium  solution  was  much  less  stable  than  the  correspon- 
ding solution  of  sulfur  and  lime,  and  its  composition  changed  so 
rapidly,  owing  to  the  deposition  of  elementary  selenium,  that  the 
results  of  the  analyses  were  very  unsatisfactory.  The  degradation 
of  the  solution  was  especially  noticeable  after  dilution  of  the 
samples  preliminary  to  their  use  in  the  titrations,  and  the  selen- 
ium that  settled  out  from  the  solution  although  red  at  first,  had 
changed  to  gray  by  the  time  it  had  collected  in  a layer  on  the  bot- 
tom of  the  beaker.  During  the  titrations  with  HG1 , the  odor  of 
hydrogen  selcnide  was  very  distinct. 

Effect  of  Varying  Proportions. 

The  proportions  used  in  the  first  lime-selenium  preparation 
were  those  required  for  the  formation  of  the  penta-selenide . The 
correct  proportions  for  production  of  the  tetraselenide  were  now 
used.  One  gram  of  CaO  was  fused  with  4.7084  gms.  of  3e.  The  re- 
sulting product  when  dissolved  in  water  gave&solution  which  was  ap- 
parently as  deep  in  color  as  the  preceding  preparation. 

For  preparation  of  the  triselenide,  1 gm.  of  CaO  was  fused 
with  3.7614  gms.  of  Se . The  color  of  the  solution  obtained  from 
this  was  red,  but  much  paler  than  before. 

When  the  right  proportions  for  the  formation  of  calcium  disel- 


10 


enici.6  (1  gm.  Ca0:2.825  gms.  of  Se ) were  used;  the  aqueous  solution 
of  the  product  was  only  slightly  colored. 

In  case  of  each  of  the  above  four  solutions,  a considerable 
amount  of  gray  sludge  remained  after  the  hot  water  extraction,  and 
the  proportion  of  undissolved  material  noticeably  increased  in  go- 
ing from  the  pentaselenide  to  the  diselenide. 

Properties. 

Sinc6  a "lime -selenium  solution"  had  evidently  been  actually 
prepared  the  next  step  was  to  try  out  its  toxic  powers.  A possi- 
ble index  of  its  promise  along  this  line  was  determined  by  means 
of  a simple  laboratory  test. 

Lab  Pests. 

Half  a dozen  small,  rectangular  glass  plates  were  equipped 
with  rubber  rings  glued  on  at  each  end  of  the  plate  and  over  these 
rings  the  sprayed  and  unsprayed  slides  were  placed  after  inocula- 
tion with  viable  spores. 

In  order  to  determine  the  strength  of  the  lime-selenium  solu- 
tion that  would  be  necessary  to  make  it  correspond  approximately 
with  the  strength  of  lime-sulfur  at  the  time  when  it  is  ready  for 
application  to  the  trees,  the  following  reasoning  was  applied:  It 

is  commonly  accepted  that,  for  practical  pur  oses,  .344  lbs.  or 
156.176  gms.  of  sulfur  per  5 gals,  of  w ter  are  required  as  a spray 
for  one  tree.  The  necessary  amount  of  selenium  would  then  be  found 
by  solving  for  x in  the  following  proportion: 

156.18:  x : :32.06:79.2. 

This  value,  385.822  gms.,  would  represent  the  quantity  of  selenium 
required  per  22,634  liters  of  water;  or  17.046  gms.  would  be  neces- 
sary for  every  liter  of  water.  Since  84.962  %,  by  weight,  of  lime- 


11 


selenium  is  selenium,  20.063  gins,  of  lime -selenium  would  be  re- 
quired for  each  liter  of  water. 

Accordingly,  for  spraying  the  slides,  approximately  2 gins,  of 
dry  lime-selenium  were  placed  on  a filter-paper  and  dissolved  as 
completely  as  possible  by  pouring  over  it  100  cc  of  boiling  hot  wa- 
ter in  lOcc  portions.  The  wine -red  solution  thus  obtained  was 
placed  in  an  atomiser  and  tiny  square  glass  plates  were  sprayed 
with  the  solution.  The  sprayed  slides  were  subjected  to  atmospher- 
ic conditions  for  24  hours,  in  order  to  approximate  the  conditions 
that  prevail  in  the  field. 

The  spores  used  in  this  particular  experiment  were  the  peni- 
cillium  glancum  and  the  aspergillius  niger.  Just  before  use,  the 
bottles  containing  the  spores  were  shaken  in  a shaking-machine  for 
ten  or  fifteen  minutes  in  order  to  ensure  an  even  distribution  of 
the  spores,  thus  rendering  counts  unnecessary.  A drop  of.  water 
from  one  of  the  bottles  was  then  placed  in  the  middle  of  each  of 
three  sprayed  and  three  unsprayed  slides  and  these  slides  were  seal- 
ed face  down  over  the  rubber  rings  on  the  glass  plates  previously 
prepared,  in  such  a way  that  the  drop  of  water  was  in  the  center 
of  the  ring.  Each  of  the  three  glass  plates  thus  carried  a sprayed 
slide  at  one  end  and  an  unsprayed  slide  at  the  other  end  to  serve 
as  a check.  In  exactly  the  same  way , the  three  other  glass  plates 
were  inoculated  with  the  other  variety  of  spores  and  all  six  plates 
were  placed  in  petri  dishes  and  set  away  for  48  hours. 

At  the  end  of  that  time,  the  slides  were  examined  carefully 
under  a microscope.  The  spores  on  the  unsprayed  slides  showed  con- 
siderable germination,  while  in  every  instance  the  sprayed  slides 
showed  either  no  germination  at  all  or  only  a slight  swelling. 


Field  Tests. 


12  . 

These  results  were  somewhat  encouraging,  hut  realising  the  un- 
reliability of  a single  laboratory  test  where  it  would  be  impossi- 
ble to  duplicate  natural  conditions  very  closely,  it  was  decided 
to  give  the  lime-selenium  a trial  on  a larger  scale.  Dr.  W. A. Ruth, 
assistant  Professor  of  Pomology  very  kindly  consented  to  subject 
the  lime-selenium  to  a field  test,  Accordingly,  two  bottles,  each 
containing  454  gms.  of  finely  powdered  lime -selenium,  were  turned 
over  to  Dr.  P.uth,  The  results  of  the  field  tests  were  much  less 
encouraging.  In  the  first  place,  considerable  difficulty  was  ex- 
perienced in  getting  the  lime -selenium  into  solution;  and  secondly, 
the  toxic  powers  of  the  spray,  did  not  measure  up  to  expectations. 
G.  Soda-Selenium  Solution: 

Preparation. 

Thinking  that  these  difficulties  might  possibly  be  obviated  if 
caustic  soda  were  substituted  for  lime  in  preparing  the  spray,  a 
"soda-selenium"  solution  was  made  by  the  simple  device  of  evaporat- 
ing down  on  the  steam  bath,  with  frequent  stirring,  97.5  gms.  of 
HaOH,  306  gms.  of  gray  selenium  and  785  cc.  of  water,  as  required 
by  the  equation: 

GIIaOH  + 12Se  ^ 2Ha2Se5  + Na2SeOg  + 3HnO. 

Properties. 

The  soda-selenium,  in  accordance  with  expectations,  could  not 
be  criticised  on  grounds  of  insolubility  as  it  dissolved  readily 
and  completely  in  water  to  a clear  mahogany-red  solution;  but  this 
advantage,  couple  1 with  any  possible  advant  s of  insecticidal  or 
fungicidal  pov/ers  were  rendered  nil  by  the  fact  that  the  caustic 
properties  of  the  solution  were  so  grea  as  to  defoliate  the  trees 


and  cause  the  fruit  to  drop 
D.  Atomic  Selenium: 


xh6  next  field  tests  were  those  made  with  "atomic  selenium" , -- 
i.e.,  the  finely  powdered  gray,  metallic  selenium;  hut  the  indica- 
tions were  that  this  material  w :s  altogether  too  coarse  in  its  na- 
ture to  he  of  any  value  as  an  insecticide  or  the  like. 

E.  Ammonium  Polyse lenide : 

Believing  that  an  ammonium  polyse lenide  prepared  after  the  an- 
alogy of  ammonium  polysulfide  might  possess  some  of  the  properties 
of  the  latter  which  render  it  efficacious  against  powdery  mildews, 
an  attempt  was  madG  to  produce  such  a solution. 

Preparation. 

Iron  selenide  was  first  prepared  hy  fusing  together  in  the 
proper  proportions  iron  filings  and  gray  selenium.  A current  of 
hydrogen  selenide,  produced  hy  dropping  dilute  sulfuric  acid  upon 
the  iron  selenide,  was  th6n  passed  through  a mixture  of  lOcc  of 
strong  ammonia  solution,  5 cc  of  distilled  water  and  9.9gms.  of  e- 
lemantary  selenium,  until  all  of  the  selenium  was  dissolved.  The 
resulting  dark  red  solution,  after  the  addition  of  strong  ammonium 
hydroxide,  constituted  the  stock  solution  from  which  the  diluted 
wash  wa3  to  he  prepared  by  dissolving  . o5  lh.  of  soft  soap  in  .995 
gals,  of  water  and  stirring  into  this. 005  gal.  of  the  stock  solu- 
tion. 

Properties. 

The  toxic  properties  of  the  ammonium  polyselenide  were  never 
determined  through  lack  of  facilities  at  the  time  for  making  the 
proper  tests;  hut  the  appearance  and  general  behavior  of  the  solu- 
tion would  lead  one  to  suspect  that  it  might  find  applications  very 


14 

similar  to  those  of  the  corresponding  ammonium  poly-sulfide. 

F.  Colloidal  Selenium: 

The  last  and  most  promising  of  the  selenium  preparations  is 
the  colloidal  red  selenium  which  is  now  undergoing  field  tests. 

Preparation. 

In  the  preparation  of  this  spray  in  quantities  sufficient  for 
application  to  one  tree,  38  gms.  of  gray  selenium  were  boiled  fear 
half  a minute  or  more  with  approximately  fifty-gram  portions  of 
crystallised  sodium  sulfite  and  about  lOOcc  of  water  until  349  gms. 
of  Ua2S03  were  used  up  and  practically  all  of  the  selenium  was  dis- 
solved, in  accordance  with  the  equation: 

ITapSOg  4 Se  > NagSeSOg. 

The  resulting  straw-colored  solution  was  - filtered , diluted  with 
water  to  5 gals.,  stirred,  35cc  of  dilute  H0SO4  added,  and  the  solu- 
tion stirred  again  vigorously.  The  chemical  reaction  here  invol- 
ved is  represented  thus: 

IlagSeSOg  4 HqS04  ^ Se  4 30g  + HgO  4 UagSOq. 

Properties . 

The  yellowish-red  solution  of  colloidal  selenium  thus  produced 
was  applied  immediately  as  a spray.  The  results  of  a single  test 
with  this  material  appeared  sufficiently  encouraging  to  warrant  the 
preparation  and  application  of  two  more  samples.  The  latest  re- 
ports from  hr.  Ruth,  dated  May  17th,  state  that  the  colloidal  selen- 
ium from  its  behavior  in  the  tests  now  being  conducted  is  promis- 
ing. This  spray,  along  with  several  other  materials,  is  being  tried 
out  on  a small  scale  in  the  commercial  orchard  on  the  University 
South  Farm.  Each  of  the  sprays  is  applied  to  one  tree.  The  col- 
loidal selenium,  according  to  the  statement  by  Dr. Ruth,  SGems  to 


. 


. 


- < 


15 


have  given  as  good  results  in  controlling  apple  scab  as  lime-sul- 
fur and  lead  arsenate  which  is  the  standard  spray.  There  was  a 
heavy  infection  of  scab  on  the  foliage  of  the  checks. 

III. 

Cone lusions . 

Significance  of  Results. 

Of  course  the  above  results,  no  matter  how  encouraging,  cannot 
be  taken  too  seriously.  Before  it  would  be  possible  to  pass  judg- 
ment definitely  with  regard  to  the  value  of  colloidal  selenium  as 
a spray,  it  would  be  necessary  to  subject  it  to  field  tests  for 
more  than  one  season,  in  different  localities,  and  under  varying 
climatic  conditions, 

Future  Possibilities. 

Perhaps  the  foregoing  description  of  experimental  work  will 
serve  better  as  an  index  of  the  possibilities  for  the  future  devel- 
opment of  selenium  and  its  compounds  than  as  a record  of  actual 
achievement.  It  is  evident  that  only  a beginning  has  been  made  a- 
long  the  line  of  determining  ways  of  utilising  selenium  in  the  ag- 
ricultural world. 

It  is  not  inconceivable  that  some  variation  in  the  methods  of 
preparation  or  application  of  the  "lime -selenium"  and  "soda-selen- 
ium" described  in  this  thesis,  might  make  all  the  difference  between 
success  and  failure  in  their  utilisation  as  insecticides  or  fungi- 
cides. For  example,  "soda-selenium",  although  too  caustic  for  many 
purposes,  might  prove  effective  as  a dormant  spray. 

It  is  possible  also  that  the  colloidal  selenium,  on  more  ex- 
tensive investigation,  may  reveal  valuable  properties  at  present  en- 
tirely beyond  our  ken. 


V 


■ 


* 


* r*\  f- 


16 


The  ammonium  polyselenide  should  he  tested  out  thoroughly  as 
a substitute  for  ammonium  polysulfide  against  powdery  milde~;s,  as 
its  success  along  this  line  would  open  up  an  entirely  new  field  of 
possibilities. 

Carbon  diselenide  might  also  be  tried  out  as  a weapon  against 
weevils  and  the  like,  because  of  the  similarity  of  its  properties 
to  those  of  carbon  disulfide. 

These  are  but  a few  of  the  possibilities  suggested  by  the  re- 
sults of  the  present  experiments,  but  they  will  serve  to  illustrate 
the  lines  of  investigation  that  are  as  yet  untouched. 

IV. 

Summary . 

1.  A lime-sulfur  solution  was  prepared  and  analysed  and  the  results 
of  the  analyses  were  found  to  agree  with  those  of  recent  chemical 
investigators  of  lime-sulfur. 

2.  An  analogous  lime-selenium  solution  was  prepared  and  its  analy- 
sis attempted,  but  the  results  were  unsat isfact ory  because  of  the 
unstable  character  of  the  solution. 

3.  The  toxicity  of  the  lime-selenium  was  tested  both  in  the  labora- 
tory and  the  field. 

4.  Laboratory  tests  indicated  that  the  lime-selenium  solution  was 
strongly  toxic. 

5.  Field  tests  failed  to  confirm  the  favorable  results  of  the  lab 
tests  because  of  the  difficulty  experienced  in  getting  the  lime-se- 
lenium into  solution. 

6.  A soda-selenium  solution  was  prepared  and  found  unsatisfactory 
as  a spray  because  of  the  strongly  caustic  properties  of  the  solu- 


tion 


17 


7.  Field  tests  indicated  that  atomic  selenium  is  too  coarse  a ma- 
terial to  he  of  value  as  an  insecticide  or  fungicide. 

8.  Ammonium  poly selenide  was  prepared  but  its  tonic  powers  were  not 

tested. 

9.  Colloidal  red  selenium  was  prepared  and  subjected  to  field  tests. 

10.  Latest  reports  indicate  that  the  colloidal  red  selenium  is  giv- 
ing as  good  results  against  apple  scab  as  lim6-sulfur  and  lead  ar- 
senate, which  is  the  standard  spray. 


